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Diagnostic Microbiology > Mycobacteria > Flashcards

Mycobacteria Flashcards

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1
Q

important human pathogens of Mycobacteria

A

○ Mycobacterium tuberculosis complex (MTBC)
○ Nontuberculosis mycobacteria (NTM)
○ Mycobacterium avium-intracellulare complex (MAI)

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2
Q

What are mycobacteria considered?

A

○ BSL 3
○ recommended .to reduce the risk of inhalation through aerosolization

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3
Q

Describe Mycobacterium

A

○ Slender, slow growing bacilli
○ Obligate aerobes
○ Cell division occurs by branching

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4
Q

How do you enhance growth of Mycobacterium?

A

Growth enhanced with CO2 (10%)

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5
Q

What is in the cell wall of Mycobacterium?

A

○ ~60% of the cell wall is comprised of lipids and lipid containing structures
○ Mycolic acid and Cord factor

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6
Q

Mycolic acid

A

○ strong hydrophobic molecules that form a lipid shell around the organism
○ affect permeability properties at the cell surface

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7
Q

What is Mycolic acid an important virulence factor for?

A

Mycobacterium tuberculosis

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8
Q

Cord Factor

A

○ responsible for the serpentine cording
○ toxic to mammalian cells
○ an inhibitor of PMN migration

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9
Q

Where is cord factor main made?

A

virulent strains of Mycobacterium tuberculosis

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10
Q

What do the high concentration of lips contribute to Mycobacterium tuberculosis?

A

○ Resistance to many antibiotics
○ Resistance to killing by acidic and alkaline compounds
○ Resistance to osmotic lysis
○ Resistance to lethal oxidations and survival inside of macrophages
○ Impermeability to stains and dyes

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11
Q

Acid-fast bacilli (AFB)

A

Mycobacteria that are difficult to decolorize when using as acid alcohol

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12
Q

What are the 3 staining methods for mycobacteria?

A

○ Ziehl-Neelsen technique
○ Kinyoun Technique
○ Fluorochrome Stain

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13
Q

Ziehl-Neelsen technique

A

○ smear is fixed and stained with hot carbol-fuchsin
○ decolorized with acid-alcohol
○ counterstained with methylene-blue
○ Acid fast bacilli appear pink in a contrasting background
○ Also this is no longer used

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14
Q

Kinyoun Technique

A

○ Similar to Ziehl-Neelsen technique but uses detergents to drive the dye into the cell wall instead of heat
○ Similar in appearance (pink contrast to background)

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15
Q

Fluorochrome Stain

A

○ uses auramine O as a primary stain
○ rhodamine as the counter stain

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16
Q

Fluorochrome stain fact

A

○ stains are more sensitive
○ more labor intensive and must be read using a fluorescent microscope

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17
Q

mycobacteria collection?

A

○ Sputums
○ Bronchial washes
○ Transtracheal aspirates

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18
Q

When do you collect mycobacteria samples? How many?

A

○ 3 samples
○ early morning preferred
○ for 3 consecutive days

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19
Q

What if a sample collection of sputum isn’t available? Like in children

A

Gastric lavage, early in the morning

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20
Q

What is done to urine samples of mycobacteria?

A

Centrifuged to concentrate

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21
Q

What fluids are collected for mycobacteria?

A

○ CSF
○ synovial fluid
○ pericardial fluid
○ peritoneal fluid

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22
Q

For blood samples, what is used to release the bacteria from red/white blood cells?

A

Lysing agents (saponin)

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23
Q

What is needed for mycobacteria processing of respiratory samples?

A

Decontamination and digestion

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24
Q

What is used for decontamination? What does it do?

A

○ NaOH or benzalkonium chloride
○ Kills normal respiratory flora or pathogens
○ reduces contaminants

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25
Q

How does NaOH work?

A

increases pH to a level that is antibacterial

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26
Q

What is used for digestion? What does it do?

A

○ N-acetyl-L-cysteine (NALC)
○ Liquefies mucus in a respiratory sample which may trap mycobacteria

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27
Q

What is needed to grow mycobacteria?

A

whole egg

28
Q

What is the traditional growth media for mycobacteria?

A

Lowenstein-Jensen Media

29
Q

Describe Lowenstein-Jensen Media

A

○ Prepared as agar slants
○ Malachite green (inhibitor)
○ Incubation 6-10 weeks
○ Can see growth as early as 18-24 days

30
Q

What is the agar based media to grow mycobacteria?

A

Middlebrook 7H10 or Middlebrook 7H11

31
Q

Describe Middlebrook 7H10/7H11

A

○ transparent
○ contains 2% glycerol to support the growth of MAC
○ Growth detected between 10-12 days

32
Q

What is Middlebrook 7H9 broth?

A

○ nonselective liquid media
○ maintains stock cultures
○ prepares isolates for biochemical analysis

33
Q

What is Mycobacterium growth index tube (MGIT)

A

○ modified 7H9 broth with a fluorchrome
○ Glows under UV light if positive

34
Q

What are the incubation temperatures for mycobacteria species?

A

○ MTB 35°C – 37°C
○ M. marinum and M. ulcerans 30°C - 32°C
○ M. xenopi 42°C – 45°C

35
Q

Are what CO2 level are mycobacterium kept at?

A

10%

36
Q

What does Mycobacterium Tuberculosis cause?

A

As the name implies, tuberculosis

37
Q

How is Mycobacterium Tuberculosis transmitted?

A

respiratory droplets containing the organism

38
Q

Once it’s inhaled, where does Mycobacterium Tuberculosis deposit?

A

bronchiole or alveoli

39
Q

For immunocompromised patients, where does Mycobacterium Tuberculosis spread?

A

○ lymph nodes
○ Spine
○ long bone
○ Heart
○ Meninges
○ gastro-urinary system

40
Q

Mantoux tuberculin skin test (TST)

A

○ used to determine if a person has been exposed to MTB organisms
○ Uses PPD that is injected into the forearm

41
Q

or Mantoux tuberculin skin test (TST), what causes false positive reactions?

A

Calmette-Guerin (BGC) vaccination

42
Q

For Mantoux tuberculin skin test (TST), what causes false negative reactions?

A

○ Suppressed immune system can cause skin test to not react
○ Recent or very old infection
○ Infants less than 6 months of age with an overwhelming TB disease

43
Q

For TST what is recommended for healthcare workers?

A

○ Two step testing is recommended
○ second TST is administered if first is negative after 1-3 weeks
○ If both tests are negative, person is fine

44
Q

QuantiFERON TB Gold In-Tube test (QFT-GIT)

A

Looks for antibodies produced from past or present infection of TB

45
Q

T-SPOT TB test (T-Spot)

A

○ Blood tests to detect TB infection
○ Can detect latent TB (nonactive TB)

46
Q

How does T-SPOT TB test (T-Spot) work?

A

When WBCs are infected with MTB a substance interferon – gamma (IFN-γ) is released and can be detected

47
Q

For MTB, what are some identifiers on LJ or Middlebrook media?

A

○ tan to buff colonies in 14-28 days at 35-37°C
○ Colony morphology is rough, dry, warty and granular (looks like breadcrumbs or cauliflower)

48
Q

What are some 1st line drugs against MTB?

A

○ Isoniazid (INH)
○ Rifampin
○ Pyrazinamide
○ Ethambuto

49
Q

What are some 2nd line drugs against MTB?

A

○ Streptomycin
○ Cycloserine
○ P-aminosalicylic acid
○ Ethionamide

50
Q

What is the mycobacterium tuberculosis complex?

A

Genetically related group of Mycobacterium species that can cause tuberculosis in humans or other organisms

51
Q

What organisms are a part of the mycobacterium tuberculosis complex?

A

○ M. tuberculosis
○ M. africanum
○ M. canettii
○ M. bovis
○ M. microti
○ M. caprae
○ M. orygis
○ M. pinnipedii

52
Q

Mycobacterium avium complex (MAC) consists of two species:

A

M. avium and M. intracellulare

53
Q

Why are the two species of MAC also called Mycobacterium avium-intracellulare (MAI)?

A

Because these species are difficult to differentiate

54
Q

Mycobacterium avium-intracellulare (MAI)

A

atypical Mycobacterium most commonly associated with human disease

55
Q

MAC is primarily a what?

A

○ pulmonary pathogen
○ affects individuals who are immune compromised

56
Q

How would you Identify MAC group?

A

○ acid-fast bacillus (AFB)
○ Colony morphology is smooth
○ tan to buff colonies in 14-28 days at 35-37°C

57
Q

M. ulcerans

A

○ produces cutaneous lesions called Buruli ulcers
○ Appear as lumps under the skin
○ non-healing ulcers

58
Q

M. ulcerans identification?

A

Flat, rough, pale colonies on LJ and Middlebrook agars at 32-33°C

59
Q

M. bovis

A

Agent of tuberculosis in cattle and other warm-blooded animals

60
Q

How has M. bovis been handled?

A

○ better pasteurization techniques
○ strict guidelines on cattle handling and management by FDA

61
Q

Bacillus Calmette–Guérin (BCG) vaccine

A

vaccine primarily used against tuberculosis in countries where tuberculosis is common

62
Q

M. leprae

A

Cause of Hansen’s disease or leprosy

63
Q

How do you grow M. leprae? And why?

A

○ grown on the foot pads of mice
○ Cannot be cultured in vitro

64
Q

M. Leprae Characterized by?

A

○ skin sores and nerve damage
○ Can get worse without treatment:
lesions on the skin
numbness in the extremities
muscle weakness

65
Q

M. leprae Identification?

A

AFB in characteristic skin lesion specimens

Diagnostic Microbiology (11 decks)

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